Final drive for driving a vehicle wheel

ABSTRACT

A brake ( 15 ) is arranged between a drive motor ( 1 ) and reduction steps ( 3, 11 ). By arranging the reduction steps ( 3, 11 ) directly adjacent one another, adequate cooling of one of the reduction steps is achieved. The wheel bearing ( 13 ) is located radially outside but axially in the area of the first reduction step ( 3 ). By this arrangement, a very compact final drive, is thereby created, in the axial direction, characterized by a favorable efficiency and ease of service.

This application is a national stage completion of PCT/EP00/09067 filedSep. 16, 2000 which claims priority from German Application Serial No.199 45 345.4 filed Sep. 22, 1999.

FIELD OF THE INVENTION

The invention relates to a final drive of a vehicle wheel.

BACKGROUND OF THE INVENTION

Final drives for driving a vehicle wheel are mainly used in low-platformbuses where each driven wheel of the vehicle has its own drive motor. Toobtain a sufficient rear width it is needed to keep as low as possiblethe axial expansion of the final drive.

DE 197 09 579 A1 has disclosed an electric single final drive havingseveral motors in which the several motors are not disposed coaxially tothe wheel axle. Via a first reduction gear drive and a second reductiongear, the output of the motors acts upon the drive wheel. A wheelbearing is situated between the first reduction step and the secondreduction step, the same as a brake disk which is additionally locatedwithin the extension of the wheel rim of a twin-tire drive wheel. Withthe wheel bearing being disposed between and separating both reductiongears there occurs, due to the displacement action of the reduction gearchiefly in helical-cut toothed wheels, a shift of the oil level. Thisdisadvantageously affects the lubrication of a reduction step. In orderto more compactly design the final drive in its axial extension and makeit possible to deliver the required torque, several electrical drivemotors have to be used.

The problem on which this invention is based is to provide a final drivefor driving a vehicle wheel. The final drive is compactly designed alongthe axis of the final drive and the brake is situated in a wheel rim,only one drive motor is used for each final drive, the reduction gear issufficiently lubricated and that stands out by a good degree ofefficiency.

SUMMARY OF THE INVENTION

According to the invention the final drive can be decelerated via abrake located within the axial extension of a wheel rim. It is possiblethat the wheel rim accommodates a single tire and the brake is placedbetween the drive motor and the reduction steps. With the reductionsteps being disposed directly adjacent, all the moving parts of thetoothing can be lubricated by lubricant which is located within a spacecommon with the reduction steps. By virtue of the arrangement of thereduction gear upon the outer side of the wheel, heat can satisfactorilyradiate to the environment, resulting in a uniform temperature level.Since the drive motor is not situated coaxially with the rotational axisof the wheel, an installation space between the wheel rim and drivemotor results and the brake and the actuation mechanism can be placedtherein. The wheel bearing is preferably disposed for absorbing thewheel forces radially above the first reduction gear so that the axialinstallation space needed by the wheel bearing is available for thedrive motor. Thereby the drive motor can be designed with a maximumactive length preferably similar or equal to the diameter of the air gapwithout the total length of the final drive being enlarged thusincreasing the degree of efficiency of the drive motor. By the wheelbearing being situated in a radial direction outside the first reductionstep but being located in the radial extension area of the firstreduction step, it is possible to connect the wheel hub, one part of thesecond reduction step and the bearing flange with the wheel bearing toform a compact unit. This compact unit does not need to be separatedeven when disassembling the wheel drive such that during assembly afterservicing, the wheel bearing does not need to be readjusted. The secondreduction step is preferably designed as a planetary gear wherein theplanet carrier of the planetary gear forms the output, the ring gear isconnected with the hub carrier which carries the wheel bearing and theinner central wheel forms the input. It is also possible to design thering gear as an output. In this case the inner central wheel is drivenby the first reduction step which is preferably designed so that thering gear forms the output and an input pinion forms the input, which isin intermeshing connection with the ring gear and at least twointermediate wheels, and the carrier which holds the intermediate wheelis non-rotatably retained. By the input pinion being in intermeshingconnection directly with the ring gear, the drive motor which drives theinput pinion can be situated at a maximum distance from the wheel axlewith the result of a sufficient installation space for the brake and theactuation mechanism of the brake. With the input pinion having anintermeshing connection with the ring gear and with at least twointermediate wheels, torque is distributed from the input pinion atmultiple locations with the consequence of an increase in the servicelife of the input pinion and the first reduction step can be morecompactly designed by reducing the diameter of the wheel bearing. Withthe housing of the drive motor transmitting the wheel forces and themounting pad of the drive motor being located in the area of the loadactive line on a hub carrier, the hub carrier carries the wheel bearingwhere the wheel forces are introduced. The connecting elements of thesupporting parts which absorb the wheel forces can be designed morecompactly , since no additional torque load from a distance to the loadactive line acts upon the mounting pad and the connecting elementsthereof. Hereby the radial extension of the mounting pad of the drivemotor housing can be compactly designed on the bearing flange such thata sealing element can be placed between the bearing flange, situated tobe non-rotatable and a wheel hub rotating at wheel rotational speedwhich has less peripheral velocities to overcome due to the small radialextension. The housing of the drive motor can either be fixed to an axlebridge or have supporting places on which fastening elements can besituated for fastening the final drive to the vehicle body. Since thedrive motor is located on the inner side of the wheel, the energy can befavorably supplied. Fins are preferably situated upon the wheel hub suchthat upon rotation of the wheel hub the medium surrounding the wheel hubis circulated so that the brake and the final drive are cooled. Acoolant preferably flows through the housing of the drive motor thuscooling the drive motor and the remaining final drive is also cooled viathe mounting pad of the drive motor.

A directly adjacent arrangement of the reduction steps and a brakesituated between the reduction steps and the drive motor but within theaxial and radial extension of a wheel rim create a final drive fordriving a vehicle wheel which stands out by a compact construction,where a drive motor with an optimum degree of efficiency can be used andthe reduction steps are sufficiently lubricated.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example, with referenceto the accompanying drawings in which:

FIG. 1 is a final drive for driving a vehicle with a double-shear planetcarrier; and

FIG. 2 is a second bearing arrangement for the final drive for driving avehicle with a double-shear planet carrier.

DETAILED DESCRIPTION OF THE INVENTION

The drive motor 1, not coaxially situated relative to the rotationalaxis of the wheel 26, is preferably an electric drive motor but may alsobe a hydraulic or pneumatic drive motor and it drives an input shaft 2which preferably passes into the housing 4 of the drive motor 1 of afirst reduction step 3. The housing 4 of the drive motor is preferablycooled by water and is connected with a hub carrier 5 via connectingelements. The hub carrier 5 is located in the area of a load active line7 along the mounting pad 6 of the drive motor 1 where the wheel forcesact upon the final drive. The longitudinal center of the tire and wheeldefine the active load line 7. The mounting pad 6 being situated in thearea of the active load line 7 so that none or only small torque loads,generated by the vehicle weight, act upon the elements which connect thehub carrier 5 with the housing 4 of the drive motor 1. The mounting pad6 can thus have a small dimension along its radial extension, it beingpossible upon this diameter to place a sealing element 8 between a wheelhub 9 rotating at the rotational speed of the wheel and the hub carrier5. Since the dimension of the radial extension of the mounting pad 6 issmall, the peripheral velocity of the sealing element 8 is also small,which advantageously acts upon the service life of the sealing element8. The wheel hub 9 is connected with the planet carrier 10 which formsthe output of a second reduction gear 11 and with a wheel rim 12. A pairof wheel bearings 13 support the wheel hub 9, the ring gear 14, thesecond reduction step 11, the sealing element 8 and the hub carrier 5 toform a unit which is adjusted only once at the plant and remainscomplete when the final drive is disassembled for servicing. A brakedisk 15 is placed over connecting elements on the wheel hub 9 by whichthe wheel hub 9 can be decelerated. The brake disk 15, which ispreferably assembled as a pair of discs fixed together, but can also beassembled as a complete brake disk, in its axial installation positionis set apart from the sealing element 8 such that a detrimental increasein temperature of the brake disk 15 does not afflict the sealing element8. Fins 16 are preferably situated on the wheel hub 9, such that uponrotation of the wheel hub 9 the medium surrounding the wheel hub 9 iscirculated so that the brake disk 15 and the complete final drive arecooled. A bearing 17 supports the inner central wheel 18 of the secondreduction step 11 upon the planet carrier 10 rotates only at thedifferential rotational speed between the inner central wheel 18 and theplanet carrier 10 whereby the service life of the bearing is increased.The bearing 17 can also be constructed as an axial thrust plate. If thefirst reduction step 3 and the second reduction step 11 have ahelical-cut design, it is possible to design the teeth of the gears sothat the bearing 17 is free of forces. The housing 4 of the drive motor1 is preferably fixed to an axle bridge 19 but can also be designedhaving fastening elements for a single-wheel suspension. The firstreduction step 3 and the second reduction step 11 are disposed directlyadjacent each other thus being surrounded by a common lubricant wherebythe lubrication lubricates both reduction steps. The wheel bearings 13are situated radially further outside the first reduction step 3 andaxially in the area of the first reduction step 3. This design creates avery compact final drive. With the wheel bearing 13 being placedradially further outside the first reduction step 3 and tapered rollerbearings being preferably used, the drive wheel is supported in a morestable manner. The input shaft 2 preferably has a recess 24 on itsexterior surface which delivers lubricant so that the motor bearing 20remains lubricated. It is also possible to eccentrically design theopening in which the input shaft 2 is situated in order to makeavailable sufficient lubrication to the motor bearing 20. The reductiongears 3 and 11 have teeth that are preferably helically-cut in order toachieve a favorable noise level. The planets 21 of the second reductiongear 11 are floatingly supported whereby the axial length of the finaldrive is further reduced.

A second embodiment of the invention will now be described with respectto FIG. 2. The embodiment of FIG. 2 differs from the embodiment of FIG.1 in at least the arrangement of the bearing 17 located between thefirst and second reduction gears. In the embodiment of FIG. 2, thebearing 17 is located on the 4 outside of the inner central wheel 18,not on the inside as with FIG. 1. A drive motor 1 drives a firstreduction step 3, the output of which drives a second reduction step 11preferably designed as planetary transmission with planet gears 21. Thering gear of the second reduction step 11 can be connected, in a radialdirection, with the hub carrier 5 either via a screw connection or viasafety rings or pins. A rotational speed sensor 22 is placed between thebrake disk 15 and the first reduction gear 3. The brake is actuated withan actuation mechanism 23 which is preferably situated on the side. Itis also possible to actuate the brake via rods extending outside theinner wheel area. The input shaft 2 of the first reduction step 3 has awinding recess, that extends along the axial length of the firstreduction step 2, which upon rotation to the input shaft 2 deliverslubrication between the first reductions step 3 and the drive motor 1.

Reference numerals

1 drive motor

2 input shaft

3 first reduction step

4 housing

5 hub carrier

6 mounting pad

7 load active line

8 sealing element

9 wheel hub

10 planet carrier

11 second reduction step

12 wheel rim

13 wheel bearing

14 ring gear

15 brake disk

16 fins

17 bearing

18 inner central wheel

19 axle bridge

20 motor bearing

21 planet gears

22 rotational speed sensor

23 actuation mechanism

24 winding recess

26 wheel

What is claimed is:
 1. A final drive for propelling a vehicle wheel, thedrive comprising: a vehicle wheel with a rim (12) defining a wheelrotational axis; a drive motor (1) having a rotational drive axis offsetwith respect to the wheel rotational axis, and the drive motor (1)driving the vehicle wheel via reduction gears (3, 11); and a disk brake(15) situated within the rim (12) for braking rotation of the vehiclewheel, and the disk brake (15) being actuated by an actuation mechanism(23); wherein the reduction gears (3, 11) comprise first and secondreduction gear sets (3, 11) which are located adjacent one another, andthe disk brake (15) is located between the drive motor (1) and the firstand second reduction gears (3, 11).
 2. The final drive according toclaim 1, wherein the actuation mechanism (23) is located adjacent thedrive motor (1).
 3. The final drive according to claim 1, wherein awheel bearing (13) radially circumscribes the first reduction gear (3)for facilitating rotation of the vehicle wheel.
 4. The final driveaccording to claim 1, wherein the second reduction gear set (11) is aplanetary gear set having a sun gear, a ring gear and a plurality ofplanet gears.
 5. The final drive according to claim 1, wherein amounting pad (6) for the drive motor (1) is located along an active loadline (7) and separates the first and second reduction gear sets (3, 11)from the drive motor (1).
 6. The final drive according to claim 1,wherein the drive motor (1) includes a housing (4) and radial forces actupon housing (4).
 7. The final drive according to claim 1, wherein thedrive motor (1) is an electromotor.
 8. The final drive according toclaim 7, wherein a fixed ring gear (14) of the second reduction gear set(11) is carried by a hub carrier (5) which is also radiallycircumscribed by the wheel bearings (13).
 9. The final drive accordingto claim 1, wherein a seal (8) is situated between a hub carrier (5) anda wheel hub (9) integral with the disk brake (15).
 10. The final driveaccording to claim 1, further comprising a wheel hub (9) having exteriorfins (16) which, upon rotation of the wheel hub (9), induces flow of acooling medium which is directed toward at least the disc brake (15) tofacilitate cooling thereof.
 11. The final drive according to claim 1,wherein the drive motor (1) is hydraulically cooled.
 12. The final driveaccording to claim 1, wherein a ring gear (14) of the second reductiongear (11), a rotatably fixed hub carrier (5), a wheel bearing (13) and aseal (18) are all combined with one another to form a single assemblyunit.
 13. The final drive according to claim 1, wherein an input shaft(2) of the first reduction gear (3) has a recess which supplieslubricant to a motor bearing (20) upon rotation of the input shaft (2).14. The final drive according to claim 1, wherein an input pinion of thefirst reduction gear (3) meshes with a ring gear of the first reductiongear (3) and an intermediate wheel of the first reduction gear (3) whichmeshes with at least one other intermediate wheel.
 15. The final driveaccording to claim 1, wherein a wheel bearing (13) has an axis skewedfrom the longitudinal axis of the wheel and motor axis.
 16. The finaldrive according to claim 1, wherein a wheel bearing (13) comprises apair of adjacent tapered bearings.
 17. A final drive for propelling avehicle wheel, the drive comprising: a drive motor (1) having at shaftextending along a drive axis, the shaft driving first and secondreduction gear set (3, 11); a wheel driven by the first and second gearsset (3, 11) rotates about a wheel axis, and the drive axis is offsetwith respect to the wheel axis; and a disk brake (15) is actuated by anactuation mechanism for braking the wheel, and the disk brake beinglocated within a rim (12) of the wheel; the first and second reductiongears sets (3, 11) are located adjacent each other and the disk brake(15) is placed between the drive motor (1) and the first and secondreduction gears (3, 11).
 18. A final drive for propelling a vehiclewheel, the drive comprising: a vehicle wheel with a rim (12) defining awheel rotational axis; a drive motor (1) having a rotational drive axisoffset with respect to the wheel rotational axis, and the drive motor(1) driving the vehicle wheel via reduction gears (3, 11); a disk brake(15) located within the rim (12) for braking rotation of the vehiclewheel, the disk brake (15) defining a brake plane extending normal tothe wheel rotational axis, and the disk brake (15) being actuated by anactuation mechanism (23); wherein the reduction gears (3, 11) comprisesfirst and second reduction gear sets (3, 11), and the drive motor (1) islocated on one side of the brake plane while the first and secondreduction gear sets (3, 11) are located on an opposite side of the brakeplane.